As Long Train Runnin said, the coupon is only valid on the rail portion of the fare. The first passenger will pay the full price of the roomette. I envision no scenario where the coupon will make a $2000 difference in the cost of travel. To investigate this for yourself, ask the Amtrak web site how much your trip would be for one person.

Independent of that, a roomette is cramped for two people, and the upper bunk (sometimes called the coffin) can be difficult to enter or exit. I (6 feet tall, 180 pounds) have trouble rolling over in the upper bunk once I'm up there. I have made multiple trips with two people in a roomette, and I expect never to do so again.